Water partitioning in Mozzarella cheese and its relationship to cheese meltability

The aim of this study was to determine what happens to water in Mozzarella cheeses during storage and to relate those changes to cheese microstructure and functionality. A reduced fat (8% fat) Mozzarella cheese and a control cheese with 19% fat were made and evaluated over 21 d of refrigerated stora ge at 4 degrees C. Fat, protein, ash, salt, and water were measured on d 1. Meltability, total water, freezable water, and expressible water were meas ured on d 1, 7, 14, and 21. Even though the reduced fat cheese had a higher total water content than did the control cheese, the reduced fat cheese co ntained less water on a fat-free basis. The amount of water expressible at 25 degrees C was higher in the control cheese than in the reduced fat chees e and was proportional to the fat content of the cheese. During storage, th e expressed serum for both cheeses decreased to zero by d 21. Based on chan ges observed in microstructure of a commercial Mozzarella cheese (19% fat) during storage, we concluded that the expressed water was derived from wate r contained in the fat-serum channels that were interspersed throughout the protein matrix. The amount of bound water was lower in the control cheese than in the reduced fat cheese and was proportional to the protein content of the cheese. Bound water levels remained constant throughout storage. Dur ing storage of the commercial Mozzarella cheese, the fat-serum channels bec ame smaller with the protein matrix expanding into the areas between the fa t globules. By d 21, the fat globules were completely encased by the protei n matrix. This expansion of the protein matrix in the commercial cheese occ urred over the same time span as the decrease in expressible water of the e xperimental cheese and indicated that the protein matrix was absorbing the water originally located in the fat-serum channels. Because no change in bo und water was observed, the water that had been expressible at d 1 was bein g absorbed into the protein matrix as entrapped water. The meltability of b oth cheeses increased during storage while the percentage of entrapped wate r increased.